lib/lz4/lz4_decompress.c

   1 /*
   2  * LZ4 - Fast LZ compression algorithm
   3  * Copyright (C) 2011 - 2016, Yann Collet.
   4  * BSD 2 - Clause License (http://www.opensource.org/licenses/bsd - license.php)
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met:
   8  *      * Redistributions of source code must retain the above copyright
   9  *        notice, this list of conditions and the following disclaimer.
  10  *      * Redistributions in binary form must reproduce the above
  11  * copyright notice, this list of conditions and the following disclaimer
  12  * in the documentation and/or other materials provided with the
  13  * distribution.
  14  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  15  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  16  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  17  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  18  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  19  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  20  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  24  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25  * You can contact the author at :
  26  *      - LZ4 homepage : http://www.lz4.org
  27  *      - LZ4 source repository : https://github.com/lz4/lz4
  28  *
  29  *      Changed for kernel usage by:
  30  *      Sven Schmidt <4sschmid@informatik.uni-hamburg.de>
  31  */
  32
  33 /*-************************************
  34  *      Dependencies
  35  **************************************/
  36 #include <linux/lz4.h>
  37 #include "lz4defs.h"
  38 #include <linux/init.h>
  39 #include <linux/module.h>
  40 #include <linux/kernel.h>
  41 #include <asm/unaligned.h>
  42
  43 /*-*****************************
  44  *      Decompression functions
  45  *******************************/
  46
  47 #define DEBUGLOG(l, ...) {}     /* disabled */
  48
  49 #ifndef assert
  50 #define assert(condition) ((void)0)
  51 #endif
  52
  53 /*
  54  * LZ4_decompress_generic() :
  55  * This generic decompression function covers all use cases.
  56  * It shall be instantiated several times, using different sets of directives.
  57  * Note that it is important for performance that this function really get inlined,
  58  * in order to remove useless branches during compilation optimization.
  59  */
  60 static FORCE_INLINE int LZ4_decompress_generic(
  61          const char * const src,
  62          char * const dst,
  63          int srcSize,
  64                 /*
  65                  * If endOnInput == endOnInputSize,
  66                  * this value is `dstCapacity`
  67                  */
  68          int outputSize,
  69          /* endOnOutputSize, endOnInputSize */
  70          endCondition_directive endOnInput,
  71          /* full, partial */
  72          earlyEnd_directive partialDecoding,
  73          /* noDict, withPrefix64k, usingExtDict */
  74          dict_directive dict,
  75          /* always <= dst, == dst when no prefix */
  76          const BYTE * const lowPrefix,
  77          /* only if dict == usingExtDict */
  78          const BYTE * const dictStart,
  79          /* note : = 0 if noDict */
  80          const size_t dictSize
  81          )
  82 {
  83         const BYTE *ip = (const BYTE *) src;
  84         const BYTE * const iend = ip + srcSize;
  85
  86         BYTE *op = (BYTE *) dst;
  87         BYTE * const oend = op + outputSize;
  88         BYTE *cpy;
  89
  90         const BYTE * const dictEnd = (const BYTE *)dictStart + dictSize;
  91         static const unsigned int inc32table[8] = {0, 1, 2, 1, 0, 4, 4, 4};
  92         static const int dec64table[8] = {0, 0, 0, -1, -4, 1, 2, 3};
  93
  94         const int safeDecode = (endOnInput == endOnInputSize);
  95         const int checkOffset = ((safeDecode) && (dictSize < (int)(64 * KB)));
  96
  97         /* Set up the "end" pointers for the shortcut. */
  98         const BYTE *const shortiend = iend -
  99                 (endOnInput ? 14 : 8) /*maxLL*/ - 2 /*offset*/;
 100         const BYTE *const shortoend = oend -
 101                 (endOnInput ? 14 : 8) /*maxLL*/ - 18 /*maxML*/;
 102
 103         DEBUGLOG(5, "%s (srcSize:%i, dstSize:%i)", __func__,
 104                  srcSize, outputSize);
 105
 106         /* Special cases */
 107         assert(lowPrefix <= op);
 108         assert(src != NULL);
 109
 110         /* Empty output buffer */
 111         if ((endOnInput) && (unlikely(outputSize == 0)))
 112                 return ((srcSize == 1) && (*ip == 0)) ? 0 : -1;
 113
 114         if ((!endOnInput) && (unlikely(outputSize == 0)))
 115                 return (*ip == 0 ? 1 : -1);
 116
 117         if ((endOnInput) && unlikely(srcSize == 0))
 118                 return -1;
 119
 120         /* Main Loop : decode sequences */
 121         while (1) {
 122                 size_t length;
 123                 const BYTE *match;
 124                 size_t offset;
 125
 126                 /* get literal length */
 127                 unsigned int const token = *ip++;
 128                 length = token>>ML_BITS;
 129
 130                 /* ip < iend before the increment */
 131                 assert(!endOnInput || ip <= iend);
 132
 133                 /*
 134                  * A two-stage shortcut for the most common case:
 135                  * 1) If the literal length is 0..14, and there is enough
 136                  * space, enter the shortcut and copy 16 bytes on behalf
 137                  * of the literals (in the fast mode, only 8 bytes can be
 138                  * safely copied this way).
 139                  * 2) Further if the match length is 4..18, copy 18 bytes
 140                  * in a similar manner; but we ensure that there's enough
 141                  * space in the output for those 18 bytes earlier, upon
 142                  * entering the shortcut (in other words, there is a
 143                  * combined check for both stages).
 144                  *
 145                  * The & in the likely() below is intentionally not && so that
 146                  * some compilers can produce better parallelized runtime code
 147                  */
 148                 if ((endOnInput ? length != RUN_MASK : length <= 8)
 149                    /*
 150                     * strictly "less than" on input, to re-enter
 151                     * the loop with at least one byte
 152                     */
 153                    && likely((endOnInput ? ip < shortiend : 1) &
 154                              (op <= shortoend))) {
 155                         /* Copy the literals */
 156                         memcpy(op, ip, endOnInput ? 16 : 8);
 157                         op += length; ip += length;
 158
 159                         /*
 160                          * The second stage:
 161                          * prepare for match copying, decode full info.
 162                          * If it doesn't work out, the info won't be wasted.
 163                          */
 164                         length = token & ML_MASK; /* match length */
 165                         offset = LZ4_readLE16(ip);
 166                         ip += 2;
 167                         match = op - offset;
 168                         assert(match <= op); /* check overflow */
 169
 170                         /* Do not deal with overlapping matches. */
 171                         if ((length != ML_MASK) &&
 172                             (offset >= 8) &&
 173                             (dict == withPrefix64k || match >= lowPrefix)) {
 174                                 /* Copy the match. */
 175                                 memcpy(op + 0, match + 0, 8);
 176                                 memcpy(op + 8, match + 8, 8);
 177                                 memcpy(op + 16, match + 16, 2);
 178                                 op += length + MINMATCH;
 179                                 /* Both stages worked, load the next token. */
 180                                 continue;
 181                         }
 182
 183                         /*
 184                          * The second stage didn't work out, but the info
 185                          * is ready. Propel it right to the point of match
 186                          * copying.
 187                          */
 188                         goto _copy_match;
 189                 }
 190
 191                 /* decode literal length */
 192                 if (length == RUN_MASK) {
 193                         unsigned int s;
 194
 195                         if (unlikely(endOnInput ? ip >= iend - RUN_MASK : 0)) {
 196                                 /* overflow detection */
 197                                 goto _output_error;
 198                         }
 199                         do {
 200                                 s = *ip++;
 201                                 length += s;
 202                         } while (likely(endOnInput
 203                                 ? ip < iend - RUN_MASK
 204                                 : 1) & (s == 255));
 205
 206                         if ((safeDecode)
 207                             && unlikely((uptrval)(op) +
 208                                         length < (uptrval)(op))) {
 209                                 /* overflow detection */
 210                                 goto _output_error;
 211                         }
 212                         if ((safeDecode)
 213                             && unlikely((uptrval)(ip) +
 214                                         length < (uptrval)(ip))) {
 215                                 /* overflow detection */
 216                                 goto _output_error;
 217                         }
 218                 }
 219
 220                 /* copy literals */
 221                 cpy = op + length;
 222                 LZ4_STATIC_ASSERT(MFLIMIT >= WILDCOPYLENGTH);
 223
 224                 if (((endOnInput) && ((cpy > oend - MFLIMIT)
 225                         || (ip + length > iend - (2 + 1 + LASTLITERALS))))
 226                         || ((!endOnInput) && (cpy > oend - WILDCOPYLENGTH))) {
 227                         if (partialDecoding) {
 228                                 if (cpy > oend) {
 229                                         /*
 230                                          * Partial decoding :
 231                                          * stop in the middle of literal segment
 232                                          */
 233                                         cpy = oend;
 234                                         length = oend - op;
 235                                 }
 236                                 if ((endOnInput)
 237                                         && (ip + length > iend)) {
 238                                         /*
 239                                          * Error :
 240                                          * read attempt beyond
 241                                          * end of input buffer
 242                                          */
 243                                         goto _output_error;
 244                                 }
 245                         } else {
 246                                 if ((!endOnInput)
 247                                         && (cpy != oend)) {
 248                                         /*
 249                                          * Error :
 250                                          * block decoding must
 251                                          * stop exactly there
 252                                          */
 253                                         goto _output_error;
 254                                 }
 255                                 if ((endOnInput)
 256                                         && ((ip + length != iend)
 257                                         || (cpy > oend))) {
 258                                         /*
 259                                          * Error :
 260                                          * input must be consumed
 261                                          */
 262                                         goto _output_error;
 263                                 }
 264                         }
 265
 266                         memcpy(op, ip, length);
 267                         ip += length;
 268                         op += length;
 269
 270                         /* Necessarily EOF, due to parsing restrictions */
 271                         if (!partialDecoding || (cpy == oend))
 272                                 break;
 273                 } else {
 274                         /* may overwrite up to WILDCOPYLENGTH beyond cpy */
 275                         LZ4_wildCopy(op, ip, cpy);
 276                         ip += length;
 277                         op = cpy;
 278                 }
 279
 280                 /* get offset */
 281                 offset = LZ4_readLE16(ip);
 282                 ip += 2;
 283                 match = op - offset;
 284
 285                 /* get matchlength */
 286                 length = token & ML_MASK;
 287
 288 _copy_match:
 289                 if ((checkOffset) && (unlikely(match + dictSize < lowPrefix))) {
 290                         /* Error : offset outside buffers */
 291                         goto _output_error;
 292                 }
 293
 294                 /* costs ~1%; silence an msan warning when offset == 0 */
 295                 /*
 296                  * note : when partialDecoding, there is no guarantee that
 297                  * at least 4 bytes remain available in output buffer
 298                  */
 299                 if (!partialDecoding) {
 300                         assert(oend > op);
 301                         assert(oend - op >= 4);
 302
 303                         LZ4_write32(op, (U32)offset);
 304                 }
 305
 306                 if (length == ML_MASK) {
 307                         unsigned int s;
 308
 309                         do {
 310                                 s = *ip++;
 311
 312                                 if ((endOnInput) && (ip > iend - LASTLITERALS))
 313                                         goto _output_error;
 314
 315                                 length += s;
 316                         } while (s == 255);
 317
 318                         if ((safeDecode)
 319                                 && unlikely(
 320                                         (uptrval)(op) + length < (uptrval)op)) {
 321                                 /* overflow detection */
 322                                 goto _output_error;
 323                         }
 324                 }
 325
 326                 length += MINMATCH;
 327
 328                 /* match starting within external dictionary */
 329                 if ((dict == usingExtDict) && (match < lowPrefix)) {
 330                         if (unlikely(op + length > oend - LASTLITERALS)) {
 331                                 /* doesn't respect parsing restriction */
 332                                 if (!partialDecoding)
 333                                         goto _output_error;
 334                                 length = min(length, (size_t)(oend - op));
 335                         }
 336
 337                         if (length <= (size_t)(lowPrefix - match)) {
 338                                 /*
 339                                  * match fits entirely within external
 340                                  * dictionary : just copy
 341                                  */
 342                                 memmove(op, dictEnd - (lowPrefix - match),
 343                                         length);
 344                                 op += length;
 345                         } else {
 346                                 /*
 347                                  * match stretches into both external
 348                                  * dictionary and current block
 349                                  */
 350                                 size_t const copySize = (size_t)(lowPrefix - match);
 351                                 size_t const restSize = length - copySize;
 352
 353                                 memcpy(op, dictEnd - copySize, copySize);
 354                                 op += copySize;
 355                                 if (restSize > (size_t)(op - lowPrefix)) {
 356                                         /* overlap copy */
 357                                         BYTE * const endOfMatch = op + restSize;
 358                                         const BYTE *copyFrom = lowPrefix;
 359
 360                                         while (op < endOfMatch)
 361                                                 *op++ = *copyFrom++;
 362                                 } else {
 363                                         memcpy(op, lowPrefix, restSize);
 364                                         op += restSize;
 365                                 }
 366                         }
 367                         continue;
 368                 }
 369
 370                 /* copy match within block */
 371                 cpy = op + length;
 372
 373                 /*
 374                  * partialDecoding :
 375                  * may not respect endBlock parsing restrictions
 376                  */
 377                 assert(op <= oend);
 378                 if (partialDecoding &&
 379                     (cpy > oend - MATCH_SAFEGUARD_DISTANCE)) {
 380                         size_t const mlen = min(length, (size_t)(oend - op));
 381                         const BYTE * const matchEnd = match + mlen;
 382                         BYTE * const copyEnd = op + mlen;
 383
 384                         if (matchEnd > op) {
 385                                 /* overlap copy */
 386                                 while (op < copyEnd)
 387                                         *op++ = *match++;
 388                         } else {
 389                                 memcpy(op, match, mlen);
 390                         }
 391                         op = copyEnd;
 392                         if (op == oend)
 393                                 break;
 394                         continue;
 395                 }
 396
 397                 if (unlikely(offset < 8)) {
 398                         op[0] = match[0];
 399                         op[1] = match[1];
 400                         op[2] = match[2];
 401                         op[3] = match[3];
 402                         match += inc32table[offset];
 403                         memcpy(op + 4, match, 4);
 404                         match -= dec64table[offset];
 405                 } else {
 406                         LZ4_copy8(op, match);
 407                         match += 8;
 408                 }
 409
 410                 op += 8;
 411
 412                 if (unlikely(cpy > oend - MATCH_SAFEGUARD_DISTANCE)) {
 413                         BYTE * const oCopyLimit = oend - (WILDCOPYLENGTH - 1);
 414
 415                         if (cpy > oend - LASTLITERALS) {
 416                                 /*
 417                                  * Error : last LASTLITERALS bytes
 418                                  * must be literals (uncompressed)
 419                                  */
 420                                 goto _output_error;
 421                         }
 422
 423                         if (op < oCopyLimit) {
 424                                 LZ4_wildCopy(op, match, oCopyLimit);
 425                                 match += oCopyLimit - op;
 426                                 op = oCopyLimit;
 427                         }
 428                         while (op < cpy)
 429                                 *op++ = *match++;
 430                 } else {
 431                         LZ4_copy8(op, match);
 432                         if (length > 16)
 433                                 LZ4_wildCopy(op + 8, match + 8, cpy);
 434                 }
 435                 op = cpy; /* wildcopy correction */
 436         }
 437
 438         /* end of decoding */
 439         if (endOnInput) {
 440                 /* Nb of output bytes decoded */
 441                 return (int) (((char *)op) - dst);
 442         } else {
 443                 /* Nb of input bytes read */
 444                 return (int) (((const char *)ip) - src);
 445         }
 446
 447         /* Overflow error detected */
 448 _output_error:
 449         return (int) (-(((const char *)ip) - src)) - 1;
 450 }
 451
 452 int LZ4_decompress_safe(const char *source, char *dest,
 453         int compressedSize, int maxDecompressedSize)
 454 {
 455         return LZ4_decompress_generic(source, dest,
 456                                       compressedSize, maxDecompressedSize,
 457                                       endOnInputSize, decode_full_block,
 458                                       noDict, (BYTE *)dest, NULL, 0);
 459 }
 460
 461 int LZ4_decompress_safe_partial(const char *src, char *dst,
 462         int compressedSize, int targetOutputSize, int dstCapacity)
 463 {
 464         dstCapacity = min(targetOutputSize, dstCapacity);
 465         return LZ4_decompress_generic(src, dst, compressedSize, dstCapacity,
 466                                       endOnInputSize, partial_decode,
 467                                       noDict, (BYTE *)dst, NULL, 0);
 468 }
 469
 470 int LZ4_decompress_fast(const char *source, char *dest, int originalSize)
 471 {
 472         return LZ4_decompress_generic(source, dest, 0, originalSize,
 473                                       endOnOutputSize, decode_full_block,
 474                                       withPrefix64k,
 475                                       (BYTE *)dest - 64 * KB, NULL, 0);
 476 }
 477
 478 /* ===== Instantiate a few more decoding cases, used more than once. ===== */
 479
 480 int LZ4_decompress_safe_withPrefix64k(const char *source, char *dest,
 481                                       int compressedSize, int maxOutputSize)
 482 {
 483         return LZ4_decompress_generic(source, dest,
 484                                       compressedSize, maxOutputSize,
 485                                       endOnInputSize, decode_full_block,
 486                                       withPrefix64k,
 487                                       (BYTE *)dest - 64 * KB, NULL, 0);
 488 }
 489
 490 static int LZ4_decompress_safe_withSmallPrefix(const char *source, char *dest,
 491                                                int compressedSize,
 492                                                int maxOutputSize,
 493                                                size_t prefixSize)
 494 {
 495         return LZ4_decompress_generic(source, dest,
 496                                       compressedSize, maxOutputSize,
 497                                       endOnInputSize, decode_full_block,
 498                                       noDict,
 499                                       (BYTE *)dest - prefixSize, NULL, 0);
 500 }
 501
 502 int LZ4_decompress_safe_forceExtDict(const char *source, char *dest,
 503                                      int compressedSize, int maxOutputSize,
 504                                      const void *dictStart, size_t dictSize)
 505 {
 506         return LZ4_decompress_generic(source, dest,
 507                                       compressedSize, maxOutputSize,
 508                                       endOnInputSize, decode_full_block,
 509                                       usingExtDict, (BYTE *)dest,
 510                                       (const BYTE *)dictStart, dictSize);
 511 }
 512
 513 static int LZ4_decompress_fast_extDict(const char *source, char *dest,
 514                                        int originalSize,
 515                                        const void *dictStart, size_t dictSize)
 516 {
 517         return LZ4_decompress_generic(source, dest,
 518                                       0, originalSize,
 519                                       endOnOutputSize, decode_full_block,
 520                                       usingExtDict, (BYTE *)dest,
 521                                       (const BYTE *)dictStart, dictSize);
 522 }
 523
 524 /*
 525  * The "double dictionary" mode, for use with e.g. ring buffers: the first part
 526  * of the dictionary is passed as prefix, and the second via dictStart + dictSize.
 527  * These routines are used only once, in LZ4_decompress_*_continue().
 528  */
 529 static FORCE_INLINE
 530 int LZ4_decompress_safe_doubleDict(const char *source, char *dest,
 531                                    int compressedSize, int maxOutputSize,
 532                                    size_t prefixSize,
 533                                    const void *dictStart, size_t dictSize)
 534 {
 535         return LZ4_decompress_generic(source, dest,
 536                                       compressedSize, maxOutputSize,
 537                                       endOnInputSize, decode_full_block,
 538                                       usingExtDict, (BYTE *)dest - prefixSize,
 539                                       (const BYTE *)dictStart, dictSize);
 540 }
 541
 542 static FORCE_INLINE
 543 int LZ4_decompress_fast_doubleDict(const char *source, char *dest,
 544                                    int originalSize, size_t prefixSize,
 545                                    const void *dictStart, size_t dictSize)
 546 {
 547         return LZ4_decompress_generic(source, dest,
 548                                       0, originalSize,
 549                                       endOnOutputSize, decode_full_block,
 550                                       usingExtDict, (BYTE *)dest - prefixSize,
 551                                       (const BYTE *)dictStart, dictSize);
 552 }
 553
 554 /* ===== streaming decompression functions ===== */
 555
 556 int LZ4_setStreamDecode(LZ4_streamDecode_t *LZ4_streamDecode,
 557         const char *dictionary, int dictSize)
 558 {
 559         LZ4_streamDecode_t_internal *lz4sd =
 560                 &LZ4_streamDecode->internal_donotuse;
 561
 562         lz4sd->prefixSize = (size_t) dictSize;
 563         lz4sd->prefixEnd = (const BYTE *) dictionary + dictSize;
 564         lz4sd->externalDict = NULL;
 565         lz4sd->extDictSize      = 0;
 566         return 1;
 567 }
 568
 569 /*
 570  * *_continue() :
 571  * These decoding functions allow decompression of multiple blocks
 572  * in "streaming" mode.
 573  * Previously decoded blocks must still be available at the memory
 574  * position where they were decoded.
 575  * If it's not possible, save the relevant part of
 576  * decoded data into a safe buffer,
 577  * and indicate where it stands using LZ4_setStreamDecode()
 578  */
 579 int LZ4_decompress_safe_continue(LZ4_streamDecode_t *LZ4_streamDecode,
 580         const char *source, char *dest, int compressedSize, int maxOutputSize)
 581 {
 582         LZ4_streamDecode_t_internal *lz4sd =
 583                 &LZ4_streamDecode->internal_donotuse;
 584         int result;
 585
 586         if (lz4sd->prefixSize == 0) {
 587                 /* The first call, no dictionary yet. */
 588                 assert(lz4sd->extDictSize == 0);
 589                 result = LZ4_decompress_safe(source, dest,
 590                         compressedSize, maxOutputSize);
 591                 if (result <= 0)
 592                         return result;
 593                 lz4sd->prefixSize = result;
 594                 lz4sd->prefixEnd = (BYTE *)dest + result;
 595         } else if (lz4sd->prefixEnd == (BYTE *)dest) {
 596                 /* They're rolling the current segment. */
 597                 if (lz4sd->prefixSize >= 64 * KB - 1)
 598                         result = LZ4_decompress_safe_withPrefix64k(source, dest,
 599                                 compressedSize, maxOutputSize);
 600                 else if (lz4sd->extDictSize == 0)
 601                         result = LZ4_decompress_safe_withSmallPrefix(source,
 602                                 dest, compressedSize, maxOutputSize,
 603                                 lz4sd->prefixSize);
 604                 else
 605                         result = LZ4_decompress_safe_doubleDict(source, dest,
 606                                 compressedSize, maxOutputSize,
 607                                 lz4sd->prefixSize,
 608                                 lz4sd->externalDict, lz4sd->extDictSize);
 609                 if (result <= 0)
 610                         return result;
 611                 lz4sd->prefixSize += result;
 612                 lz4sd->prefixEnd  += result;
 613         } else {
 614                 /*
 615                  * The buffer wraps around, or they're
 616                  * switching to another buffer.
 617                  */
 618                 lz4sd->extDictSize = lz4sd->prefixSize;
 619                 lz4sd->externalDict = lz4sd->prefixEnd - lz4sd->extDictSize;
 620                 result = LZ4_decompress_safe_forceExtDict(source, dest,
 621                         compressedSize, maxOutputSize,
 622                         lz4sd->externalDict, lz4sd->extDictSize);
 623                 if (result <= 0)
 624                         return result;
 625                 lz4sd->prefixSize = result;
 626                 lz4sd->prefixEnd  = (BYTE *)dest + result;
 627         }
 628
 629         return result;
 630 }
 631
 632 int LZ4_decompress_fast_continue(LZ4_streamDecode_t *LZ4_streamDecode,
 633         const char *source, char *dest, int originalSize)
 634 {
 635         LZ4_streamDecode_t_internal *lz4sd = &LZ4_streamDecode->internal_donotuse;
 636         int result;
 637
 638         if (lz4sd->prefixSize == 0) {
 639                 assert(lz4sd->extDictSize == 0);
 640                 result = LZ4_decompress_fast(source, dest, originalSize);
 641                 if (result <= 0)
 642                         return result;
 643                 lz4sd->prefixSize = originalSize;
 644                 lz4sd->prefixEnd = (BYTE *)dest + originalSize;
 645         } else if (lz4sd->prefixEnd == (BYTE *)dest) {
 646                 if (lz4sd->prefixSize >= 64 * KB - 1 ||
 647                     lz4sd->extDictSize == 0)
 648                         result = LZ4_decompress_fast(source, dest,
 649                                                      originalSize);
 650                 else
 651                         result = LZ4_decompress_fast_doubleDict(source, dest,
 652                                 originalSize, lz4sd->prefixSize,
 653                                 lz4sd->externalDict, lz4sd->extDictSize);
 654                 if (result <= 0)
 655                         return result;
 656                 lz4sd->prefixSize += originalSize;
 657                 lz4sd->prefixEnd  += originalSize;
 658         } else {
 659                 lz4sd->extDictSize = lz4sd->prefixSize;
 660                 lz4sd->externalDict = lz4sd->prefixEnd - lz4sd->extDictSize;
 661                 result = LZ4_decompress_fast_extDict(source, dest,
 662                         originalSize, lz4sd->externalDict, lz4sd->extDictSize);
 663                 if (result <= 0)
 664                         return result;
 665                 lz4sd->prefixSize = originalSize;
 666                 lz4sd->prefixEnd = (BYTE *)dest + originalSize;
 667         }
 668         return result;
 669 }
 670
 671 int LZ4_decompress_safe_usingDict(const char *source, char *dest,
 672                                   int compressedSize, int maxOutputSize,
 673                                   const char *dictStart, int dictSize)
 674 {
 675         if (dictSize == 0)
 676                 return LZ4_decompress_safe(source, dest,
 677                                            compressedSize, maxOutputSize);
 678         if (dictStart+dictSize == dest) {
 679                 if (dictSize >= 64 * KB - 1)
 680                         return LZ4_decompress_safe_withPrefix64k(source, dest,
 681                                 compressedSize, maxOutputSize);
 682                 return LZ4_decompress_safe_withSmallPrefix(source, dest,
 683                         compressedSize, maxOutputSize, dictSize);
 684         }
 685         return LZ4_decompress_safe_forceExtDict(source, dest,
 686                 compressedSize, maxOutputSize, dictStart, dictSize);
 687 }
 688
 689 int LZ4_decompress_fast_usingDict(const char *source, char *dest,
 690                                   int originalSize,
 691                                   const char *dictStart, int dictSize)
 692 {
 693         if (dictSize == 0 || dictStart + dictSize == dest)
 694                 return LZ4_decompress_fast(source, dest, originalSize);
 695
 696         return LZ4_decompress_fast_extDict(source, dest, originalSize,
 697                 dictStart, dictSize);
 698 }
 699
 700 #ifndef STATIC
 701 EXPORT_SYMBOL(LZ4_decompress_safe);
 702 EXPORT_SYMBOL(LZ4_decompress_safe_partial);
 703 EXPORT_SYMBOL(LZ4_decompress_fast);
 704 EXPORT_SYMBOL(LZ4_setStreamDecode);
 705 EXPORT_SYMBOL(LZ4_decompress_safe_continue);
 706 EXPORT_SYMBOL(LZ4_decompress_fast_continue);
 707 EXPORT_SYMBOL(LZ4_decompress_safe_usingDict);
 708 EXPORT_SYMBOL(LZ4_decompress_fast_usingDict);
 709
 710 MODULE_LICENSE("Dual BSD/GPL");
 711 MODULE_DESCRIPTION("LZ4 decompressor");
 712 #endif